<!DOCTYPE html>
<html lang="en">
<head>
    <title>Document</title>
<style>
  #outer {
    padding: 20px;
    background: #616161;
  }

  #inner {
    width: 100px;
    height: 100px;
    background: #757575;
  }
</style>
</head>
<body>
    
<div id="outer">
  <div id="inner"></div>
</div>

<script type="text/javascript">
const $inner = document.querySelector('#inner')
const $outer = document.querySelector('#outer')

function handler () {
  console.log('click') // 直接输出

  Promise.resolve().then(_ => console.log('promise')) // 注册微任务

  setTimeout(_ => console.log('timeout')) // 注册宏任务

  requestAnimationFrame(_ => console.log('animationFrame')) // 注册宏任务

  $outer.setAttribute('data-random', Math.random()) // DOM属性修改，触发微任务
}

new MutationObserver(_ => {
  console.log('observer')
}).observe($outer, {
  attributes: true
})

$inner.addEventListener('click', handler)
$outer.addEventListener('click', handler)
</script>

</body>
</html>